Answers:
C9: SUM(C2:C8). This is an addition, the ":" makes the sum expand from C2 all the way to C8 and add all the numbers together. When we do "SUM(C2+C8)" we are just making the simple sum between cells C2 and C8.
D3: C3/C9.This is a division, because it's a relative frequency.
D7: C7/C9.This is a division, because it's a relative frequency.